In recent years, demands for printing on packages, textiles, and product decorations have increased. Inkjet printing is more advantageous than form-based printing in a small lot production and a shorter lead time. For this reason, the inkjet printing is regarded as a printing technique suitable for packages, textiles, and product decorations.
A liquid-droplet ejection head of inkjet printing includes an actuator for ejecting ink. The actuator employs, as a driver, a piezoelectric element in which electrodes are disposed on both major surfaces of a piezoelectric film mainly containing lead zirconate titanate.
Printing objects, such as packages, textiles, and product decorations have a less flat printing surface than printing objects, such as printing paper. Moreover, printing objects, such as packages, textiles, and product decorations, require more varieties of inks than printing objects, such as printing paper.
For this reason, the piezoelectric element requires higher piezoelectric performance so that the printing objects with non-flat printing surfaces can be printed at high speed and high resolution with various types of inks. A conventional technique for increasing the piezoelectric constant of lead zirconate titanate is the technique in which the piezoelectric film is made to have (001) preferential orientation and also lead zirconate titanate is doped with niobium in an amount of 10 mole % to 40 mole %.
Conventional techniques relating to the aforementioned piezoelectric element are disclosed in, e.g. PTLs 1-6.
Niobium-doped lead zirconate titanate may cause an internal electric field in the piezoelectric element.
A driver is often employed in a form of an actuator in which a substrate, a lower electrode, a piezoelectric film, and an upper electrode are stacked on one another. In the case that the piezoelectric film of this actuator is made of niobium-doped lead zirconate titanate, an internal electric field is produced in a direction from the lower electrode toward the upper electrode. For example, the value of the internal electric field, which is read from the polarization-electric field curve (P-E curve) disclosed in FIG. 7 of PTL 4, is 18 kV/cm.
NPL 1 describes that a sample having an internal electric field of 10-15 kV/cm causes, under a continuous operation, polarization deterioration earlier than a sample having no internal electric field.
PTLs 4 and 5 disclose a technique of reducing the internal electric field of the piezoelectric film by substituting lead ions with bismuth ions.
PTL 6 discloses a piezoelectric film in which the mole ratio of lead with respect to that of the cations other than lead is set to equal to or less than 1.03.